1. Field of the Invention
This invention relates to an electrically conductive adhesive, a method for the manufacture thereof, and a bio-medical electrode using the electrically conductive adhesive as an essential component thereof.
2. Description of Prior Art
The electrode to be used for the living body has been known in the the field of clinical medicine. Generally, the electrode of this class is provided with an electrically conductive material such as a metallic plate having a conductive wire connected thereto. This wire is connected to a therapeutic apparatus or to a medical measuring instrument. At times, an electrically conductive paste, cream, or gel is applied to the skin of a patient for the purpose of improving electric connection between the skin of the patient and the electrically conductive material such as an electrode. The electrically conductive paste, cream, or gel which has been used to date for this purpose is slimy and offensive. This practice of using such material entails the troublesome chore of removing the material after use by wiping. There are persons who receive unpleasant stimulus from the wiping action.
To improve the situation, the so-called dry-type electrode using an electrically conductive adhesive as its basic component has been developed. In this dry electrode, the electrically conductive adhesive serves the purpose of enhancing the conductivity of electricity between the skin and the electrode and ensuring adhesion of the electrode to the skin. One known version of this dry electrode utilizes an adhesive agent incorporating therein an electrically conductive filler formed of particles of metal or metal salt. This version has a problem concerning the ability to transmit electric signals.
Another known version of the dry electrode makes use of a natural polymer such as karaya rubber. The natural polymer is liable to be affected by such factors as origin and weather conditions and it does not easily acquire a constant quality owing to variability of its content of impurities. In the circumstance, studies have been under way in search of an electrically conductive synthetic polymer suitable for an adhesive agent in the dry electrode. As synthetic polymers of this nature, there have been proposed an adhesive incorporating therein a cohesive synthetic hydrophilic polymer containing at least 5 mol % of a carboxylate monomer unit, lacking a stimulating property, and enjoying high adaptability (U.S. Pat. No. 4,273,135), an adhesive agent formed of a water-soluble monomer, a nonionic water-soluble interpolymer of a water-soluble monomer with a water-insoluble monomer, or a nonionic water-insoluble interpolymer of a water-soluble monomer with a water-insoluble monomer containing at least 15% of water-soluble monomer (Japanese Patent Laid-open No. SHO 56(1981)-36,940), and an electrically conductive adhesive obtained by radically polymerizing a water-soluble polyhydric alcohol, an unsaturated carboxylate soluble in the polyhydric alcohol, and a radically polymerizable polyfunctional unsaturated monomer (WO81/02097).
The disadvantage constitutes one of the reasons for the persistent demand for a dry electrode. In consequence of the diversification of the manner of use, there are times when the polymer is left standing in a state randomly taken out of its package. In this case, there is the possibility that the aging has its adverse effects manifested upon various essential properties of the polymer such as coming into fast adhesion to the patient's skin under a slight pressure, resisting separation from the skin due to the patient's perspiration or movement, having adequate softness for adhering closely with the skin of the patient despite a complicated shape without a gap, and not tending to leave any residue of the adhesive agent behind on the patient's skin after use. There are times when it becomes necessary for the polymer taken out of its package to be provisionally coated on its surface with a film for the purpose of preservation of cleanliness. Incidentally, the dry electrode utilizing the polymer requires for its packaging the use of a film which has been treated with a peeling agent. None of the electrodes so far developed is readily applied to and separated from the conventional film which has not been given the aforementioned treatment.
An object of this invention, therefore, is to provide a novel electrically conductive adhesive and a method for the manufacture thereof.
Another object of this invention is to provide a bio-medical electrode using the novel electrically conductive adhesive as its essential component.